Aluminum alloy welding refers to the process of welding aluminum alloy materials. The aluminum alloy is high in strength and light in weight. The main welding processes are manual MIG welding (molten inert gas shielded welding) and automatic MIG welding, and its base metal, welding wire, shielding gas and welding equipment.
Aluminum alloy welding production storage environment and requirements for the use of auxiliary materials
1. Requirements for production storage temperature and humidity
The production and storage environment of aluminum alloy must be dustproof, waterproof and dry. The ambient temperature is usually controlled above 5 °C and the humidity is controlled below 70%.
It should be ensured that the humidity of the welding environment should not be too high. If the humidity is too high, the probability of occurrence of pores in the weld will increase significantly, thus affecting the welding quality. The violent flow of air causes insufficient gas protection, resulting in weld vents, and a windshield can be provided to avoid the effects of indoor winds.
2. The use of welding wire and air supply hose requirements
The use of welding consumables should be noted that the aluminum welding wire should be stored separately from the steel welding consumables, and the service life should not exceed 1a. After the welding is completed, the wire is taken out in the welder for sealing treatment to prevent contamination. The air supply hoses of different materials have different resistance to moisture ingress, especially when the air supply pressure is high, and the influence of the air supply hose is more obvious. It is best to use a Teflon hose for the air supply hose.
3. The selection of tooling
Aluminum alloy welding is best done in the form of point contact to reduce the contact area between the tool and the workpiece. If the tooling is in surface contact with the workpiece, it will quickly take away the heat of the workpiece and accelerate the solidification of the molten pool, which is not conducive to the elimination of weld pores. 5 MPa。 The pressure of the tooling hydraulic system is preferably controlled at 9~9. 5 MPa.
If the pressure is too small, the purpose of the preset anti-deformation will not be achieved, but if the pressure is too large, the degree of restraint of the aluminum alloy structure will increase. Due to the large coefficient of linear expansion of the aluminum alloy, the high temperature plasticity is poor, and large thermal stress is easily generated during welding, which may cause cracks in the aluminum alloy structure.
Welding wire selection
For the 6005A, 6082, and 5083 base metals, the selected wire grade is 5087/ AlMg4. 5MnZr, and the 5087 wire not only has good crack resistance, excellent resistance to porosity, but also good strength properties. For the selection of wire specifications, the wire of large diameter is preferred. The same welding filling amount is the same weight of the welding wire, the surface area of the small size welding wire of the large size welding wire is much smaller. Therefore, the surface contamination of the small specification welding wire is small, that is, the oxidation area is small, and the welding quality is easier to meet the requirements. . In addition, the wire feeding process of large diameter wire is easier to handle. For a base material having a thickness of 8 mm or less, a welding wire of 1.2 mm diameter is generally used, and for a base material having a thickness of 8 mm or more, a welding wire of 1.6 mm diameter is used. The automatic welding machine uses a welding wire of 1.6 mm diameter.
Selection of shielding gas
Ar100% is characterized by stable arc and easy arc ignition. For base metals with a thickness of 8mm or less, Ar100% is generally used for welding. For base metal with a thickness of 8 mm and above and welds with high porosity, Ar70 % + He30 % is used for welding. The characteristics of helium are: 9 times the thermal conductivity of argon, the welding speed is faster, the porosity is reduced, and the penetration is increased. For thick plate welding, the penetration of Ar100% and Ar70%+He30% is shown in Figure 1. The gas flow rate selection is not as large as possible, and the flow rate is too large to cause turbulence, resulting in insufficient protection of the molten pool, and the reaction of the air with the deposited metal changes the weld structure, degrades performance, and the tendency to produce welded pores increases.
Preparation before welding
1. The treatment of the groove
Butt welds with a thickness of less than 3 mm can be opened without a bevel. Simply pour a corner of 0.5 to 1 mm on the back of the weld to facilitate gas discharge and avoid back grooves. Whether the back surface has the effect of chamfering on the weld, the groove angle of the aluminum alloy thick plate is larger than that of the steel plate. The single-edge groove generally adopts a 55° groove, and the double-sided groove adopts a 35° groove on each side. This improves the accessibility of the weld and reduces the chance of unfused defects.
For HV or HY joints in thick T-joints, it is required to fill the groove and add a fillet weld so that the total weld size S is not less than the thickness T.
2. Cleaning work before welding
Welding aluminum alloys requires the cleanest preparation, otherwise the corrosion resistance is reduced and the pores are easily generated. Welded aluminum alloys should be completely differentiated from the habit of welding steel. A tool that has been used for welding steel and is strictly prohibited when welding aluminum alloy. Clean up oxides such as oxide film in the weld area, and use stainless steel brushes or acetone as much as possible. Grinding can not be done with a grinding wheel, because grinding with a grinding wheel will only fuse the oxide film to the surface of the welding material without actually removing it. And if a hard grinding wheel is used, the impurities will enter the weld and cause hot cracks. In addition, since the Al2O3 film is regenerated and accumulated in a very short time, in order to make the oxide film affect the weld as little as possible, it should be applied immediately after cleaning.
3. Preheating temperature and interlayer temperature control
For welding with thick plates with a thickness of more than 8 mm, pre-weld preheating is required. The preheating temperature is controlled between 80 °C and 120 °C, and the interlayer temperature is controlled between 60 °C and 100 °C. If the preheating temperature is too high, in addition to the harsh working environment, it may affect the alloy properties of the aluminum alloy, and the joint softens and the appearance of the weld bead is poor. Excessive temperature between layers also increases the probability of hot cracking of aluminum solder.
4. Reasonable selection of normative parameters
The physicochemical properties of aluminum alloy and steel are very different, and the welding specification parameters should be tested and determined according to the welding characteristics of aluminum alloy.
5. The welding current is larger
The aluminum alloy itself has a large thermal conductivity (about 4 times that of steel) and it dissipates heat quickly. Therefore, at the same welding speed, the heat input when welding aluminum alloy is 2 to 4 times larger than the heat input when welding steel. If the amount of heat input is not enough, there is a problem that the penetration is insufficient or even not fused, especially at the position where the weld starts.
6. The wire feed speed should be properly increased
The wire feeding speed is closely related to the specification parameters such as current and voltage, and matches each other. When the welding current is increased, the wire feed speed should also be increased accordingly.
7. The choice of welding speed
For thin plate welds, in order to avoid overheating of the weld, a smaller welding current and a faster welding speed are generally used; for thick plate welds, a larger weld is used in order to fully weld the weld and fully escape the weld gas. Current and slower welding speed.
8. The choice of welding gun angle
In the welding direction, the angle of the welding torch is generally controlled at about 90°. Too large and too small will cause welding defects. If the angle of the welding torch is too large, the gas protection is insufficient and the air hole is generated; if the angle is too small, the liquid aluminum may reach the front end of the arc, so that the arc cannot directly act on the weld seam to cause unfusion.
1. Remove the oxides on the groove and surrounding parts of the workpiece and the surface of the wire by mechanical or chemical methods before welding;
2. Use a qualified protective gas for protection during the welding process;
3. In the gas welding, the flux is used, and the oxide film on the surface of the molten pool is continuously scraped by the welding wire during the welding process.
1. The socket of copper and aluminum tubes in the refrigeration industry, the heterogeneous welding of central air-conditioning copper and galvanized pipes, stainless steel pipes and aluminum pipes.
2. Welding of copper and aluminum terminals, copper and aluminum leads, and copper and aluminum conductive rows in the substation industry.
3. Welding of radiator tubes, motors and busbars in the electronic and electrical industry.
4. It is also used in the production of faucets, coupling connectors, matching nuts, etc. in life.
Post weld cleaning
1. Carefully scrub the welded joints with a hard brush in hot water.
2. Dip the weldment in a solution of chromic anhydride or potassium dichromate at a temperature of 60-80 ° C and a mass fraction of 2% to 3% for about 5 to 10 minutes, and wash it carefully with a hard brush. Or the weldment is immersed in a 10% to 20 °C 10% nitric acid solution for 10-20 minutes.
3. Wash the weldment in hot water.
4. Dry the weldment with hot air or dry it in a 100 °C dry box.
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